This invention relates to a laminated ceramic device utilizing an electrostrictive effect and a method of manufacturing the same and more particularly it relates to a laminated ceramic device that can prevent concentration of stress due to unevenly distributed strain caused by application of an electric field and therefore is suitably used for an actuator or a similar application as well as to a method of manufacturing the same.
As is well known, a laminated ceramic device utilizing an electrostrictive effect is suitably used for an actuator or a similar application. FIGS. 7(A) and 7(B) of the accompanying drawings illustrate a typical laminated ceramic device designed as actuator.
In FIG. 7(A), it is shown that a laminated ceramic device generally indicated by reference numeral 2 comprises a number of ceramic sheets 4 arranged in so many layers with filmy internal electrodes 6a, 6b interposed therebetween. When viewed in cross section as in FIG. 7(A), the internal electrodes 6a, 6b are arranged obliquely relative to the two adjacent internal electrodes, a group consisting of every other electrodes 6a and the other group of electrodes 6b being respectively connected with corresponding external electrodes 8a, 8b. When a certain voltage is applied to the external electrodes 8a, 8b, a ceramic device 2 with such an arrangement of internal electrodes 6a, 6b and external electrodes 8a, 8b gives rise to an electric field in a direction perpendicular to the ceramic sheets 4 so that the ceramic device 2 is deformed in the directions of arrow A under the effect of the electric field and functions as an actuator.
In a laminated ceramic device 2 of this known type, those areas portion 10 of the layered ceramic sheets that are not intersected by internal electrodes 6a, 6b are inseparable from one another.
However, a laminated ceramic device 2 of this known type has a drawback of concentration of stress taking place at the boundary of portion 12, which exists between the internal electrodes 6a and 6b, and portion 10 which exists between only the internal electrodes 6a and 6a or 6b and 6b, because the portion 12 which exists between the internal electrodes 6a and 6b is strongly affected by the electric field generated by the applied voltage, whereas the portion 10 which exists between only the internal electrodes 6a and 6a, or 6b and 6b is weakly affected by the electric field. Such concentration of stress can significantly reduce the durability of the laminated ceramic device 2.
With a view to eliminating such a drawback, Japanese Patent Laid Open 58-196068 and 59-175176 propose a laminated ceramic device as illustrated in FIG. 8(A) and 8(B), wherein said laminated ceramic device 2a comprises filmy internal electrodes 6, each of which is interposed between two adjacent ceramic sheets 4 from end to end, insulation layers 14, each of which is arranged at an edge of every other internal electrode, and a pair of external electrodes 8a, 8b arranged at the two lateral sides of the device to cover the insulation layers. Since each of the internal electrodes 6 is so interposed between two adjacent ceramic sheets as to cover the whole surface areas thereof, all the ceramic sheets contained in the device 2a are evenly affected by an electric field applied thereto in the direction perpendicular to the sheets. Therefore a laminated ceramic device 2a comprising ceramic sheets 4 and having a configuration as illustrated in FIGS. 8(A) and 8(B) is free from concentration of stress that can take place in a device of FIGS. 7(A) and 7(B) and accordingly can expect an improved durability.
On the other hand, however, a laminated ceramic device 2a of FIGS. 8(A) and 8(B) requires a relatively complicated manufacturing process as each of the insulation layers 14 is arranged at an edge of every other internal electrode 6, making the process rather inefficient and consequently pushing up the manufacturing cost of the product. Moreover, if such a device has a defectively formed insulation layer in it, the two external electrodes 8a, 8b can be short-circuited to make the device inoperative.